AMENDMENT TO THE TRUST UNDER THE SUPPLEMENTAL EXECUTIVE RETIREMENT PLAN OF WITCO CORPORATION AND THE EXCESS BENEFIT AND COMPENSATION CAP PLAN OF WITCO CORPORATION

                                                                  Exhibit 10(iv)

                                    AMENDMENT
                       TO THE TRUST UNDER THE SUPPLEMENTAL
                          EXECUTIVE RETIREMENT PLAN OF
                              WITCO CORPORATION AND
                 THE EXCESS BENEFIT AND COMPENSATION CAP PLAN OF
                                WITCO CORPORATION

                  WHEREAS, Witco Corporation (the "Company") is considering
entering into the Agreement and Plan of Reorganization by and among Crompton &
Xxxxxxx Corporation, Park Merger Co. and the Company (the "Merger Agreement");
and

                  WHEREAS, the Company has determined that the transactions
contemplated by the Merger Agreement should be considered a "Change in Control"
of the Company for purposes of the Trust under the Supplemental Executive
Retirement Plan of Witco Corporation and the Excess Benefit and Compensation
Plan of Witco Corporation (the "Trust").

                  NOW THEREFORE, the Company hereby amends the Trust Agreement
as follows:

                  1. The definition of "Change in Control" contained in the
Trust Agreement is hereby amended by adding the following to the end thereof:

                  Notwithstanding anything to the contrary contained herein, a
                  merger, consolidation, reorganization or other business
                  combination involving the Company and Crompton & Xxxxxxx
                  Corporation ("C&K") or any affiliate of C&K shall be
                  considered a "Change in Control" for all purposes of the
                  Trust.

                  2. Section 2(f) of the Trust Agreement is hereby amended by
deleting "Upon a Change in Control, the Company shall, as soon as possible, but
in no event later than 30 days following the Change the Change in Control" from
the first sentence thereof and substituting the following thereof:

                  As soon as reasonably practicable after the Company has reason
                  to believe a Change in Control has occurred or, in the
                  immediate future, will occur, the Company shall

                  3. Section 2(f) of the Trust Agreement is hereby amended by
adding the following to the end thereof:

                  In the event the Company makes a contribution to the Trust in
                  anticipation of a Change in Control and the Board







                                                       Exhibit 10(iv)(continued)

subsequently determines that such Change in Control is not reasonably likely to
occur, the Trustee shall return to the Company the portion of the contribution
designated by the Board.

                  4. Section 13(a) of the Trust Agreement is deleting the first
proviso thereof and substituting the following therefor:

                  provided, however that Sections 2(f), 3, 11(c), 11(d), 12(b)
                  and 13(a) of this Trust Agreement may not be amended by the
                  Company for 10 years following a Change in Control.

                  IN WITNESS WHEREOF, the Company has caused this Amendment to
be executed as of the date set forth below.


                                              WITCO CORPORATION,


                                              /s/ X. Xxxx Xxxx
                                              ----------------------------------
                                              Name:  X. Xxxx Xxxx
                                              Title: Chairman, President and
                                                         CEO


Date:  May 31, 1999
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